HAC1 regulates flowering time via non-histone acetylation in Arabidopsis

C.M. HUA, Q. SHEN, L.S. SHEN, H. YU

Department of Biological sciences, National University of Singapore, 21 Lower Kent Ridge Rd 117543, Singapore

HAC1 is a p300/CBP histone acetyltransferase that affects flowering time in Arabidopsis. Although previous studies have demonstrated the role of HAC1 in histone acetylation, its enzyme activity towards non-histone proteins have yet to be investigated. In this study, we show that HAC1 interacts with and acetylates HACP (HAC1-acetylating protein), which subsequently inhibits FLC mRNA expression. HACP binds to the FLC intron 1, but its binding affinity is decreased in hac1-6 mutants, indicating that HAC1 promotes HACP binding to the FLC intron 1. We also found that the splicing efficiency of FLC intron 1 is increased in hac1-6 mutants and that HACP inhibits splicing of the FLC intron 1 through possibly interacting with the splicing factor SR45. In addition, we observed that acetylation of HACP by HAC1 affects splicing efficiency of the FLC intron 1. Our findings so far suggest that HAC1 acetylates HACP, which may facilitate HACP to and inhibit the splicing efficiency of the FLC intron1 via HACP interaction with SR45, thus downregulating FLC expression and promoting flowering time in Arabidopsis.